1. Related Application
This application is related to "IMPROVED PERFORATED END PLUG PLATE FOR TESTING CORE SAMPLES", Ser. No. 651561 filed concurrently with this application.
2. Field of the Invention
The present invention relates to a method and apparatus for ascertaining the permeability and/or porosity of core samples from an underlying rock formation and, more particularly, to a method and apparatus for automatically testing a number of such core samples.
3. Background of the Art
Two important parameters for evaluating production of an underlying oil or gas bearing formation are the permeability and porosity of core samples actually taken from the formation. A measurement of permeability of the core provides an indication as to how fast the oil or gas will flow from the formation upon production whereas a measurement porosity provides information as to the amount of oil or gas contained within the formation. The determination of both porosity and permeability are based upon complex mathematical determinations and both are common measurements in the oil and gas industry.
An understanding of these mathematical formulas is not necessary for the understanding of the present invention. However, a discussion of the mathematical formulas for determining Klinkenberg permeability, the Klinkenberg slip factor and the Forcheimer tubulence factor observed in core plugs is set forth in the inventor's prior publication entitled "A Rapid Accurate Unsteady-State Klinkenberg Permeameter", Society of Petroleum Engineers Journal, October, 1972, Pages 383-397. In that publication, a method and apparatus for performing permeability tests on core samples is set forth. In that disclosure, each sample core is manually loaded into a Hassler core holder and the sleeve contained therein is then pressurized to simulate an overburden pressure. A gas, such as nitrogen, is then introduced into one end of the core and the passage of the gas through the core is then determined to ascertain the permeability.
In addition, prior to the filing of this invention, a patentability search was conducted which uncovered the following patents:
______________________________________ Inventor Reg. No. Reg. Date ______________________________________ Bowman 966,078 Aug. 2, 1910 Dietert et al. 2,516,188 July 25, 1950 Reichertz 2,539,355 Jan. 23, 1951 Leas 2,618,151 Nov. 18, 1952 Herzog et al. 2,737,804 Mar. 13, 1956 Dotson 2,745,057 May 8, 1956 Donaldson 3,158,020 Nov. 24, 1964 Heuer, Jr. et al. 3,199,341 Aug. 10, 1965 McMillen 3,839,899 Oct. 8, 1974 Wilkins 4,043,407 Aug. 23, 1977 Turner et al. 4,083,228 Apr. 11, 1978 Neri 4,227,397 Oct. 14, 1980 Wiley 4,253,327 Mar. 3, 1981 Heitmann et al. 4,287,754 Sept. 8, 1981 Pezzi 4,403,501 Sept. 13, 1983 Hains 4,430,890 Feb. 14, 1984 Holt 4,454,095 June 12, 1984 ______________________________________
The Wiley patent sets forth a method and apparatus for measuring core permeability at overburden conditions of both pressure and temperature. Furthermore, Wiley teaches the injection of the actual fluid from the formation, as well as the injection of other fluids such as corrosion inhibitors and polymers for secondary and tertiary recovery. Each core must be manually loaded into a sleeve having end plugs inserted into the sleeve. Then the entire assembly is placed into a hydrostatic cell wherein hydraulic fluid is pressurized around the end plugs and the sleeve to simulate the overburden pressure. The fluid is then injected through one end plug, through a sintered plate, through the core, out a second sintered plate and through the opposing end plug. The differential pressure is measured so that the permeability of the core can be determined.
The Herzog et al. patent provides relative permeability measurements on core samples contained in a core holder which positions each core sample in a plastic sleeve mounted within a metal cylinder so that the ends of the core sample can be subjected to various tests. The core is not placed under an overburden stress either radially or axially. The core sample must be manually loaded into the plastic sleeve which in turn threadedly engages the metal cylinder and, which must then be mounted into the core holder.
In Leas, a manually loaded cell for measuring relative permeability is disclosed wherein a flexible elastic sleeve selectively pressurizes the sides of the core during testing so as to simulate overburden stress. Fluids are injected into the end of the core to measure the permeability of the core. To insert or remove the core, a vacuum is pulled around the elastic sleeve so that the core can be manually removed or inserted. Porous disks are placed on each end of the core to aid in the distribution of the fluid to and from the core.
The Dotson patent sets forth a core sample holder which is also mechanically or manually assembled for each core measurement for determining interstitial water content and electrical resistivity wherein pressurized fluid may be introduced in a reservoir around the core positioned in the cell.
In the McMillen patent, a testing cell for determining the length, diameter, porosity, and permeability of a core sample in a single handling operation is set forth. The testing cell receives the cylindrical core sample through one end and a quick locking/releasing plug is connected over the core sample on that end. The opposing plug slidedly engages the other end of the core sample by means of a hydraulically actuated piston. The length that the piston travels is used to determine the length of the core sample. In addition, an elastic sleeve similar to that disclosed in Leas is expanded, by means of fluid pressure, around the core sample. The amount of fluid required is mathematically related to the diameter of the core and, hence, the diameter of the core can be determined.
Heuer, Jr. et al. discloses a method and apparatus for measuring compressibility of core samples by encapsulating the core sample in a fluid-impervious sheet such as flexible plastic and then suspending the core sample in a pressure vessel and subjecting the sample to high pressure while passing fluids to and from opposing ends of the core sample through perforated disks.
The Morgan patent sets forth a method of sealing cores while determining the permeability of the core by providing a counter-pressure environment around the core with an atmosphere of non-wetting fluid. The pressure eliminates the use of sealing material such as pitch, tar, or a separate sealing medium such as plastic or rubber.
The patents to Reichertz, Dietert et al., Donaldson, and Hains all relate to variations of the above approaches or to different types of tests.
The Bowman and Wilkins patents set forth approaches for mechanically holding a number of soil or core samples for conducting tests on.
The Holt patent although not related to the field of this invention, sets forth an automatic chemical analysis device utilizing a carousel to automatically position encased glass ampoules over an injection piston for selective insertion into a smashing unit for breaking the top of the ampoule. The insertion of the ampoule into the smashing chamber results in a sealed engagement of the ampoule with the chamber. Once the ampoule is smashed, a chemical analysis is performed on the contents of the ampoule.
While also not relating to the field of this invention, the search also uncovered the patents to Pezzi, Neri, ahd Heitmann, et al. which all relate to carousel-type machines for testing cigarettes including the air permeability of the cigarettes.
None of the above patents set forth a method and apparatus for automatically determining the permeability and porosity of multiple core samples wherein each core sample is automatically loaded into a testing cell and wherein the two tests are conducted automatically. The McMillen patent sets forth a cell which is manually loaded and, once manually loaded, is capable of automatically performing length, diameter, permeability, and porosity tests. However, between each set of tests, the McMillen cell must be manually disassembled to remove the core sample.
The present invention provides an automatic carousel loading apparatus and method which positions each core sample of a multiple number of core samples, each of varying length but of relatively constant diameter, above a lower piston which when activated moves the core sample upwardly into the testing cell. Once inserted into the testing cell, the piston holds the core sample in a sealed chamber and, simultaneously, axial stress and radial stress, applied by two different sources, is placed on the core sample. A second piston, internal to the first piston, selectively opens and closes the lower end of the core sample holder to conduct permeability and porosity tests, respectively. Once these tests are automatically performed, the first piston is released to lower the core sample back into the carousel, the carousel turns and the piston inserts the next core sample into the testing chamber. In this fashion, all core samples in the testing chamber are sequentially tested for permeability and porosity without manual loading. This represents a savings of a substantial amount of time on the part of a skilled operator which savings were recognized in McMillen patent as being clearly beneficial. It is not uncommon for laboratories involved in this type of testing to conduct permeability and/or porosity tests on ten to thirty thousand core samples monthly.